A chimney of height 25 m is used to provide natural draught. The ambient temperature is 25°C and the temperature of the hot gases inside the chimney is 352°C. If the discharge though the chimney is maximum determine the mass of air supplied per kg of fuel burnt.

18.54 kg of air/kg of fuel burnt

20.55 kg of air/kg of fuel burnt

18.54 kg of air/kg of fuel burnt

15.23 kg of air/kg of fuel burnt

25.21 kg of air/kg of fuel burnt

Which of the following expressions represents the correct ratio of absolute temperature of the chimney gases and absolute temperature of outside air when the discharge through the chimney is maximum.

\(\frac{T_g}{T_a} = 2(\frac{m_a+1}{m_a }) \)

\(\frac{T_g}{T_a} = \frac{m_a+1}{m_a} \)

\(\frac{T_g}{T_a} = \frac{m_a}{m_a+1} \)

\(\frac{T_g}{T_a} = 2(\frac{m_a+1}{m_a }) \)

15 + Mcqs in Natural Draught in Thermal Engineering Page 1 McqOptions

1.	Determine the ambient temperature if the temperature of flue gases inside the chimney is 363°C and the 20 kg of air is supplied for complete combustion of 1 kg of fuel. The discharge though the chimney is maximum.
A.	27°C
B.	35°C
C.	30°C
D.	25°C
Answer» D. 25°C

Discussion

2.	A chimney is used to develop natural draught of 20 mm of water. The ambient temperature is 30°C. Determine the chimney height if the discharge though the chimney is maximum.
A.	25.36 m
B.	34.33 m
C.	45.32 m
D.	41.32 m
Answer» C. 45.32 m

Discussion

3.	The temperature of flue gases was observed to be 350°C with a chimney (natural draught) of 45 m. The same draught was developed using an induced draught fan and the temperature of the flue gases was measured to be 150°C. The mass of air supplied for complete combustion of 1 kg of fuel is 20 kg. The ambient temperature is 30°C. Assuming cp = 1.004 kJ/kg for flue gases calculate the efficiency of chimney.
A.	0.21%
B.	0.56%
C.	1.23%
D.	0.11%
Answer» B. 0.56%

Discussion

4.	A boiler has a chimney of height 45 m. The ambient temperature is 25°C. The temperature of the hot gases inside chimney is 330°C. Calculate the draught in terms of column of water if it is given that discharge through the chimney is maximum.
A.	40.23 m
B.	35.45 m
C.	26.65 m
D.	24.32 m
Answer» D. 24.32 m

Discussion

5.	A chimney of height 45 m is full of hot gases at temperature 330°C. If the discharge through the chimney is maximum, determine the draught in terms of column of hot gases. The ambient is 25°C.
A.	45 m
B.	35 m
C.	25 m
D.	39 m
Answer» B. 35 m

Discussion

6.	Determine the temperature of hot gases inside the chimney if the temperature of cold air outside is 27°C and 20 kg of air is required for complete combustion of 1 kg of fuel. It is given that the discharge though the chimney is maximum.
A.	335°C
B.	300°C
C.	318°C
D.	357°C
Answer» E.

Discussion

7.	A chimney of height 25 m is used to provide natural draught. The ambient temperature is 25°C and the temperature of the hot gases inside the chimney is 352°C. If the discharge though the chimney is maximum determine the mass of air supplied per kg of fuel burnt.
A.	20.55 kg of air/kg of fuel burnt
B.	18.54 kg of air/kg of fuel burnt
C.	15.23 kg of air/kg of fuel burnt
D.	25.21 kg of air/kg of fuel burnt
Answer» B. 18.54 kg of air/kg of fuel burnt

Discussion

8.	The draught produced by the chimney is due to the difference in densities between the column of hot gases inside the chimney and the cold air present outside.
A.	True
B.	False
Answer» B. False

Discussion

9.	The frictional resistance offered to the flow of flue gases by the grate and gas passages result in draught losses.
A.	True
B.	False
Answer» B. False

Discussion

10.	What is the ratio of draught in terms of column of hot gases to the chimney height when the discharge though chimney is maximum?
A.	2
B.	1.5
C.	1.0
D.	0.5
Answer» D. 0.5

Discussion

11.	Which of the following expressions represents the correct ratio of absolute temperature of the chimney gases and absolute temperature of outside air when the discharge through the chimney is maximum.
A.	\(\frac{T_g}{T_a} = \frac{m_a+1}{m_a} \)
B.	\(\frac{T_g}{T_a} = \frac{m_a}{m_a+1} \)
C.	\(\frac{T_g}{T_a} = 2(\frac{m_a+1}{m_a }) \)
D.	\(\frac{T_g}{T_a} = 2(\frac{m_a+1}{m_a }) \)
Answer» D. \(\frac{T_g}{T_a} = 2(\frac{m_a+1}{m_a }) \)

Discussion

12.	The velocity and temperature of flue gases passing through a chimney are 20 m/s and 330°C. 18 kg of air is supplied for complete combustion of 1 kg of fuel. The ambient temperature is 27°C. Determine the chimney height 40% of the theoretical draught is lost in friction at the grate and passage.
A.	58.32 m
B.	37.57 m
C.	29.65 m
D.	35.26 m
Answer» C. 29.65 m

Discussion

13.	The velocity of flue gases though chimney is 23 m/s. The chimney height is 35 m. The temperature of the flue gases is 300°C. The flue gases formed per kg of fuel burnt is 23 kg. Find out the ambient temperature.
A.	30°C
B.	27°C
C.	40°C
D.	37°C
Answer» E.

Discussion

14.	A chimney has a height 30 m. The ambient temperature and the temperature of hot gases inside the chimney are 27°C and 300°C respectively. Find the velocity of the flue gases passing through the chimney if 50% of the theoretical draught is lost in friction at the grate and passage. It is given that 20 kg of air is required for complete combustion of 1 kg of fuel.
A.	21.35 m/s
B.	20.65 m/s
C.	15.52 m/s
D.	10.32 m/s
Answer» D. 10.32 m/s

Discussion

15.	A 25 m high chimney is filled with hot gases of temperature 330°C. The temperature of outside air is 27°C. If 20 kg of air is supplied for complete combustion of 1 kg of fuel, calculate the velocity of hot gases though the chimney.
A.	21.18 m/s
B.	25.65 m/s
C.	18.56 m/s
D.	15.65 m/s
Answer» B. 25.65 m/s

Discussion

Explore topic-wise MCQs in Thermal Engineering.

Determine the ambient temperature if the temperature of flue gases inside the chimney is 363°C and the 20 kg of air is supplied for complete combustion of 1 kg of fuel. The discharge though the chimney is maximum.

A chimney is used to develop natural draught of 20 mm of water. The ambient temperature is 30°C. Determine the chimney height if the discharge though the chimney is maximum.

A boiler has a chimney of height 45 m. The ambient temperature is 25°C. The temperature of the hot gases inside chimney is 330°C. Calculate the draught in terms of column of water if it is given that discharge through the chimney is maximum.

A chimney of height 45 m is full of hot gases at temperature 330°C. If the discharge through the chimney is maximum, determine the draught in terms of column of hot gases. The ambient is 25°C.

Determine the temperature of hot gases inside the chimney if the temperature of cold air outside is 27°C and 20 kg of air is required for complete combustion of 1 kg of fuel. It is given that the discharge though the chimney is maximum.

A chimney of height 25 m is used to provide natural draught. The ambient temperature is 25°C and the temperature of the hot gases inside the chimney is 352°C. If the discharge though the chimney is maximum determine the mass of air supplied per kg of fuel burnt.

The draught produced by the chimney is due to the difference in densities between the column of hot gases inside the chimney and the cold air present outside.

The frictional resistance offered to the flow of flue gases by the grate and gas passages result in draught losses.

What is the ratio of draught in terms of column of hot gases to the chimney height when the discharge though chimney is maximum?

Which of the following expressions represents the correct ratio of absolute temperature of the chimney gases and absolute temperature of outside air when the discharge through the chimney is maximum.

The velocity and temperature of flue gases passing through a chimney are 20 m/s and 330°C. 18 kg of air is supplied for complete combustion of 1 kg of fuel. The ambient temperature is 27°C. Determine the chimney height 40% of the theoretical draught is lost in friction at the grate and passage.

The velocity of flue gases though chimney is 23 m/s. The chimney height is 35 m. The temperature of the flue gases is 300°C. The flue gases formed per kg of fuel burnt is 23 kg. Find out the ambient temperature.

A 25 m high chimney is filled with hot gases of temperature 330°C. The temperature of outside air is 27°C. If 20 kg of air is supplied for complete combustion of 1 kg of fuel, calculate the velocity of hot gases though the chimney.